fix plot dl2 metrics

[vuillaut]

There was an error in the order of the quantities since ctaplot v0.6.

[codecov]

Codecov Report

Merging #993 (7a9c1ce) into master (60a330c) will not change coverage.
The diff coverage is 75.00%.

@@           Coverage Diff           @@
##           master     #993   +/-   ##
=======================================
  Coverage   85.75%   85.75%           
=======================================
  Files          78       78           
  Lines        6619     6619           
=======================================
  Hits         5676     5676           
  Misses        943      943           

Impacted Files	Coverage Δ
lstchain/visualization/plot_dl2.py	50.33% <75.00%> (ø)

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